Electrochemical anticorrosion performance evaluation of Al 2O 3 coatings deposited by MOCVD on an industrial brass substrate

Abstract

Alumina (Al 2O 3) coatings of different thickness were deposited on OT59 brass substrate (BS) using the metal organic chemical vapour deposition (MOCVD) technique to evaluate the corrosion performance by EIS measurements. The used precursor was dimethyl-aluminium-isopropoxide. Electrochemical characterizations of the deposited films were performed in a standard very aggressive acidic solution (aerated 1N H 2SO 4 at 25 °C up to 168 h of immersion time) by means of direct current method (Tafel curves) and electrochemical impedance spectroscopy (EIS). The Rutherford backscattering spectroscopy (RBS) indicated that the films are very pure with the correct Al 2O 3 stoichiometry, while the IR absorption spectra showed that the films did not contain any O H groups. The surface film morphology was investigated by atomic force microscopy (AFM) and displayed a globular texture. The films were very smooth, with a maximum root mean square roughness, for example, of 14 nm for a 0.96 μm thick coating. The EIS data confirmed, as expected, that a 2.40 μm Al 2O 3 layer ensures the best corrosion protection after 168 h of immersion in the very acidic environment used.